Power-operated interlocking system



Aug. 18,1925.

W; K. HOWE POWER OPERATED INTERLOCKING SYSTEM Filed Jan. 21. 19,22

2 Sheets-Sheet 1 -INV TOR; w/z.

fi/ATTORNEY.

2 Sheets-Sheet 2 w. K. HOWE POWER OPERATED INTERLOCKING SYSTEM Filed Jan. 2;. 1922 ATTORNEY.

Aug. 18, 1925.

wrnmrmor KEITH now E on New Y'o' RK; itss'ierron so: Ra -IL: WAYI SIGNAL ooMPAivY, 'OF'iGArEs"; New YORKLA CORPORATION or New 'YoRK.

Pow-ER-oBEm-mn InriiiiineoKINe' stIsTEMn Applicationafileitfi'amiztnjtl,1922, I Serial No.-530,- 8475.

To all whom it mag 0042001142.;

Be it I known. that. 1,1 iNTrmorQKn-L rm Hows, a citizen of the 'United. States ,otg'

America, iresidingpat: Rochester, in the.

countyzof Monroe and State .of New York;

have invented. certain" new and uset-ullmf.

provements in Power-Operated. Interlock.

interlocking systems forrrail-roads;iandmore' -der trains. I I r I In order to safe guard:the'movementof particularly .to a scheme. ofd'ete'ctor looking for preventing the throwingzot switches un.-

switches, or derails, andassureisafe movement of I trains throughterminals yards, and the like, where a poweroperated;inter-"- locking system is 6Il1PlOy6d,--lln is -desirable for reasons; .well recognized -.in; the art. to provide suitableautomatidmeaiis; for pre; venting a I switch being shifted byr powerunder a train or directly-injront ofaanqap proaching train; Lever locks; commonly employed for this purpose, havetheendisad;

vantage that the operator.may sometimes release them by. l1and,.-or with the" aid-hot the manual release ordinarily provided; th s obtaining control of the switcli machi-ne and I then thoughtlessly. or carelessly: manipulate the lever so as to .apply power-to thesvvitch machine at'the wrong time]; Instead otsuch lever looks, or. preferably. in; addition there; to, it is proposed. in accordance withzthis' invention to provide automatic 7 meansfor directly controlling the. application. .ofgp'ower to the switchv operating anechmisin inL-acg cordance with the condition of .thedetector track circuit, so that when .thisx.detector track circuit is occupied, poaver :isfcutofi from the .switchmachine, and-the machine can not be operated irrespective of the position of the lever: r

In a restricted sense-,rthe -present :invenf tion deals more particularly withawell knowntype of an allelectric interlocking system employing dynamic. indication and supplying the. operatingcurrent, subject to the control of the lever, from .a central source at .thetower over operating wires-to the: respective switch machines. In..this type of system, aswell; as othertypes ofsystemszcharacterized by. a similar. methodlof operation,-'.it a train sh'onldlhappento enter the detector track circuit just after the lever has been] shifted v and. betore the core. responding switch machine..=has hadtime. to operate, the. interruptionofeoperatingr. current to this switch machinewould;.with. out anything else, stop the switch machine at an intermediate pointsin its operation and leave the switchinmid-stroke .or unlocked.

The I possiblev occurrence of such a condi-.

tion,even. though it .canexist only under exceptional circumstances,- is of course. ob-

jectionable and f dangerous; and rather than. have a switch. in lmid-stroke or unlocked,:.it. is. generally better: to allow it :to complete whatever cycle of oper' ation mayhave been started; before the. entrance of a train .int'o controlling track circuit. rACCO IdlDglyflIhlSf invention contemplates an organization of parts and circuits for influenci11g-',tlie desired control of the. switch machine. from .a: track. circuit,

but .always permitting. the switch machine to complete a cycle of operation under. way regardlessvota subsequent entrance .of' a train into thetrack circuit,,nooperation bee ing possible,:however,v itthe .t'raincente'r's the tracl rjcircuit. before gthe operation of tllGSWltCh machine.,isfstarted. 1 tliistcon nection it is further considered desirabl'e'jto take away-1 1 6. operatoflsfcgontroll over. the

switch-machine assoon as a'train enters the detector trackv circuit, and while {permitting the switch machinezto completeaii operation it may *liavestar'ted, prevent the; operator from stopping or changing'this 'cycleoi": op.- eration, more especially manipulating the lever so asto work the switch machine back and. forth .between thev ends of its st roke. Various other features and advantages lot the invention will be pointed out, :and others .will be apparent, as a detail'zdescription progresses.

Indescribing the invention, reference will be made. to the"v accompanying drawings, in Which. v

Figure 1- illustrates ina siinplifiedlanol diagrammatic nanner'the parts and circuits ofa wellrknown type of anall electric initerlocking system employing: dynamic'indication and showingthe. organization ofparts and circuits constituting the invention Fig. 2 is a sideelevation ofone specific form of indication selector employed Fin connection :With this invention;

Fig. 3 is a top plan view of this indication selector, parts being broken away for the sake of clearness; and

4 is a vertical transverse section through the indication selector on the line For the purpose of more clearly illustrating the nature of this invention and facilitating explanation of the construction and mode of operation, there is shown in the accompanying drawings in a simplified and conventional way the significant parts and circuits of one particular type of a power operated interlocking system, employing a switch operating mechanism disclosed, for example, in my prior Patent, No. 1,288,595, Dec. 24, 1918. It should be understood that this specific type of interlocking system is merely illustrative of the nature and utility of the present invention, and that the invention may be applied to analogous types of system by making appropriate change in mechanical and electrical details.

Referring to Fig. 1, a stretch of track T, with a switch A is shown conventionally. The track rails 1 and 2 are divided by insulated joints 3 and bonded in the usual way to provide a detector track circuit, having a track battery 4 and a track relay 5 with a contact finger or armature 6. The movable points of the switch A are locked and shifted back and forth by a switch machine SM connected thereto in the usual way; and since the detail construction of this switch machine is fully disclosed in my prior patent above mentioned, only those parts directly involved in consideration and explanation of the present invention are illustrated, these parts being inclosed within the dotted rectangle 7. These parts include the operating motor, which comprises armature 8 and field 9, a circuit controller C for governing the operating and indication circuits, pole changer coils E for operating the circuit controller 0, and a similar circuit controller D for governing the circuits for these pole changer coils.

The circuit controller C comprises a contact block 10 of suitable insulating mate rial, carrying conducting bars or strips 11 and 12 which are adapted to bridge pairs of contact springs 13 to 16. This block 10 is operated mechanically from an extreme position shown to its other opposite extreme position by the final locking movement of the locking plunger of the switch machine, in the manner fully explained in my prior patent. In other words, this contact block is shifted mechanically from one extreme position to the other upon the completion of the cycle of operation of the switch machine. Also, this block 10 may be shifted to one extreme position or the other by energization of the corresponding pairs of pole changer coils E, said block being disengaged from its mechanical operating means at intermediate points in the cycle of operation of the machine.

The circuit controller D comprises an insulating block 17 shiftable back and forth and carries two conducting bars 18 and 19 adapted to be bridged and electrically connected by said bars. This block 17 is shifted mechanically in concurrence with the operation of the switch machine, and is moved from its existing extreme position during the unlocking movement of the switch machine to an intermediate position, connecting both pairs of contact springs 2021, until the switch machine has completed its cycle of operation and is again locked, whereupon said block is automatically shifted to its opposite extreme position.

The parts of the interlocking system located at the tower or central control point are enclosed in a dotted rectangle 22, and in general comprises the usual lever L, which is slidable back and forth and is connected to a rod 23 working insulated contact blocks 24 and 25 into and out of engagement with pairs of contact springs 26 to 29. A cam slot 30 in this lever L drives a roller on the upper end of a tappet bar 31 which is connected to the usual mechanical interlocking between this lever and other levers making up the complete machine. The lever L is provided with a handle for facilitating it movement, and associated with this handle is a latch operating angle lever 32. WVhen this latch lever 32 is pressed inward, it raises a button 33 of insulating material which operates a latch contact 34, which controls the energizing circuit for an electric lever lock F. This lock F comprises an iron clad solenoid 35, the core 36 of which carries a lock dog adapted to engage shoulders of notches 37 formed on the upper edge of the lever L. The indication latch for he lever L is designated 38, the indication magnet 39, the safety magnet 40, polarized cross protection relay P, and the main battery B, these parts being of the usual well-known construction and those commonly employed in a direct current dynamic indication type of system illustrated. The indication selector IS,however, in order to carry out the present invention, is modified somewhat in construction as compared with that ordinarily em ployed, this modified construction being shown in detail in Figs. 2 to 4.

Referring to Figs. 2 to 4, the indication selector comprises a rectangular open frame 41 of iron, to the ends of which are fastened coils 42 and 43. Disposed between these coils is an armature 44 which is pivotally supported near its upper end by a shaft 45 (see Fig. 4) fastened therein by a small transverse pin and journaled in holes in upstanding ears or lugs 41 integral with the The armature 44sisnpr'ovided at itslowelv memoir upper longitudinal member otthe fraim'e end with spring looking for; fover c'enter tl11TOW111g"rCl6V1( /G.' As shown ythls device =-co1nprisesi a. pair of plnngers 4L6 whichhawe" their heads-i pivotally mounted: on' a pin 47 fixed in the, lower end; of: the armature 44,- and which-slide in holes in a rocking ber 48 supported: byend trunnions resting in notches in the base of the frame 411,. com- 1 pression springs i9 being interposed between the rockingme-mber 48- andthe heads of the plunger 46; It will be evident that-the ten--= sion 0fthesprings 4:9 tendsto' hold the armaturei l int-he extreme positioir in: which it may be placed thereby maintaining the desired contact pressurebetween the con-- tacts assoc-iatedwithithe armature andf=l1e1felnafter described, and" also preventing dis? placement of the armature by arand: v1-

bration when its controlling coils aflor 43;

are cleenergizedr Also, the springs 49 act to force the" armature 44 to its entremepositioir as soon as it' is shifted slightly beyond its middle position in one direotionlorirthe other.

The armature i li opens. and closes certain; contacts as, it is shiftedback/and-fortlr In; the construction shown, two contact fingers 50and 51 are clamped tmthebifuncatedup-r per end: of the armaturew lli by a' plate 52aandi screws 53, these fingersibelinginsulated from the armature and from 1 each other; by inter:- posed pieces of fiber orother suitable: inf sulating material in Ull6 WZLYJSl1OWxIL; Tofthe fingers 5O' and 51 are riveted- -sidedownward ly extending split arms 54 and 5-5 respecfives l'y, which rub aga-inst-the-edge of stationary springs 56' and 57*respeotiively: To the-endsof the frame-41 are;fastenediterminaliblocks 58 and 59 of suitable insulating material;

one of which supports the sprii1gs-56%57,-

and each carrying-contact pieces i60itarranged' to' be engaged bythevendsas the: fingers. 50- and 51 The':'circuit -c'onnections; are made between the" springs- 56+57,.rto the fingers 505'1 and thence to the contact pieces; 60, with which' 's'ai'dfingers are in engagement, as shown in a simplified-and diagrammatic manner"in li i g; 1;

One characteristic-of this-specific con:- struction of indication selecton IS which adapter-it for use in conneoteionawi-tb the present invention: 'is-, =tha-t its coils 1 42%?) are i of relatively" high resistance, @in P1336? tioe usually; 251olims, so: that when 7 one," of;

these 'ooils 1 is connected iinoseries; with; the; I

ClFCllltSi devicesvconstituting the; inven tion= comprises-la suitableifrelayi Rfwhich is controlled byrtheatracki relay; 5? Thenpar; tioular circuit: shown forthe relay R,jcom

prising a separate battery atpthepswitch, "is

:- mere'ly" illustrative, avarious =other arrangements of; circuits for rendering! the energliiw zation of the" relay; Ri dependent? iu'pon the: 4 track relay. 5 being; familiar =to those skilledh 7 intlieart; The relay R isessentially a: re peatin'g relay for: .the clBteCtDrrtraek; circuit, is and inp'ractice'may bean indicatingior con, trol relay commonlylocated atjnthe t-oweriin' interlockingcsystems for exertingjhedesired 76 control for, various schemesofrapproaoh; and) route. locl'zing, operation oi indicators, track diagra1ns,-eto.-' This relay 1% is :1 shown' 38:1 providedv with; two contact fingers; 615-621 and associated frontcontacts:- The fronti contact 6210f the relay R COIltIOlSuthQ-QDGXEHJ gizing circuit forthe lever lockwF and: the! front. contact 61 controls the .energization of] the coils 4:2 and/i3 of the-indication selector IS' in a manner more fully, explained here i 8551? inaften leis noted here thatrthearelayR may be controlled by anumberiof trackc-in-e cuits, or the two cirouits taken through the front contactsqof this relay R may bertaken through the frontoontacts oral number 0t relays" governed by track circuits, according-g 1y as the varyingoperating conditionsfogr: difierent installationsm'ay require I Operat'ionz Referring; torage 1; i assume that: the parts and! circuits iOfl the; system are; in" the normal iconditionvshowni- ,Vhen; the? operator desires to; reverse; the; -switchJAi, he: presses the latch releasing; lever thereby; closing the latch contacts 34 and energizing; the locking solenoid; 35 providing,;the detector gtrack" circuit is-mot, occupied? so; that relay; R- -;-is; energized.- Afterl releasing the electric lever loclg, the --operator: then pull the leverL- out-@, (to thenleftasshown); tovits reverse indication position, whefre tlie contact bloeksr2 l+25{are moveob tocelectri cally connect the pairs of; contactwsprings- 2.6%27, thereby establishing; a reerseoper ating circuit which maiybeatraoed 1as follows-c: 'commencing'at thevbattery 13,,wire 1T0 64;,safety'magnet 40, wires 65"andr66,. front contact 61 of relay R, wires-67i and 68, coil 43 of indicationselecton-twiresfitl and; 70,

contact springs 27;, wire 71- to: reverse 1 opens ating wire 7-2, through; springs.- 14 andnban 12, ires 73 and-74 armature8, wires 75 and 76,,springsl3 and'bar 11, ,wires 77 and78, field? 9,, its common vwire'79, through-contacts; 805 or the polarized relay P ,andwire 81 back to the=batteryBi a On account;.of1the resistance of indication selector'coil 43 included thiscircnit the current flowing through the ;arm-ature 1 and field of the-switclrmagchi-nemotor isnot: sufficient to operate, the, iswitohj machine; but the current flowing; in i said coil. A3 attracts armaturei 44" of the indication, I selector. and rocks vyitscontact fingers 5O;51. togtheb other extreme position thereby ;'establishing ;a shunt around corresponding coil 43 and also the front contact 61 of relay R, this shunt being traced as follows: commencing at. wire 65, Wire 82, finger 51 in the other extreme position and wire 83 to wire 70, and

thence through contact springs 27, etc., asv

in the circuit previously traced. Sufficient current now flows to the operating motor to cause operation of the switch machine, reverse the switch points, and lock them in their new position. At the completion of the cycle of operation of the switch machine, contact block 10 of the circuit controller C is shifted to the extreme position opposite to that shown, breaking the operating circuit hereinafter traced at the contact springs 131d, and electrically connecting the contact springs 15-16 to establish the reverse indication circuit. This indication circuit includes the armature 8 and field 9 of the motor, with their connections reversed, the indication magnet 39, and contact finger 50 of the indication selector, this circuit being conveniently traced as follows: Starting at the upper brush of armature 8, wires 74 and 8d, springs 15 and bar 11, wire 78, field 9, common wire 79, contacts of polarized relay P, wire 85, winding of relay P, wire 86, indication magnet 39, wire 87, finger 50 of indication selector (previously shifted to its other extreme position), wire 88, springs 26, and block 24:, wire 89, normal operating wire 90, springs 16, and bar 12, and wires 91 and 7 5 back to the lower brush of the armature 8.

Indication current which is generated dynamically by the operating motor in the usual way, energizes indication magnet 39, releases indication latch 38, and permits the operator to complete the movement of the lever L to its full reverse position and release the mechanical interlocking associated with conflicting levers, all in the usual way characteristic of this type of system. The operation of returning the switch A back to the position shown, is the same as described, and analogous circuits, which can be readily traced, are involved.

In the foregoing operation it has been assumed that the relay R is energized, a condition existing only when the detector track circuit or circuits are unoccupied. Assume then that a train is present on the detector track circuit protecting the switch A at the time the operator desires to reverse the switch. In the first place, the electric lever lock can not be released, since the relay R is deenergized; but in addition to this protection commonly provided, the present invention also prevents the application of current to the switch machine, so that even if the operator should plug the lever lock, or obtain its release by a push button or other manual release, the switch machine can not be operated. This additional protection is afforded by the fact that the next operating circuit is broken at the front contact 61 of relay B. To explain more fully, suppose the switch machine is in the normal position shown in Fig. 1, and that front contact 61 of relay R is open, due to tliepresence of a train on the detector track circuit. If the operator should succeed in getting the lever to the reverse indication position, no current can be supplied to the operating motor, because the connection between battery B and the reverse operating wire 72 is broken at the finger 51 of the indication selector, and because the energizing circuit for coil 13 of the indication selector, capable of closing this break, is broken at the front contact 61 of relay R. Consequently, independently of the protection provided by the electric lever lock, the switch can not be changed from its existing position when there is a train present on its associated detector track circuit.

Under exceptional circumstances, it may happen that the operator releases the electric lock, shifts the lever L, and starts the operation of the switch machine just before the train enters the detector track circuit, or at least just before the relay R is operated by the entrance of such a train. Under these circumstances it is preferable to complete the cycle of operation of the switch machine that has been started, rather than stop the switch machine in mid-stroke and leave the switch points partly open or unlocked. This desirable function is accomplished by this invention, because once the indication selector has responded, the front contact 61 of relay R, as well as the corresponding coil 42 or 43, is shunted, so that current may continue to flow to the operating motor in spite of the deenergization of relay R.

It may happen that the operator for some reason desires to reverse the. switch machine in mid-stroke, and to do this he restores the lever L to the former position, thereby energizing the other operating wire and sending current through one of the pairs of pole changer coils E, contact block 17 of circuit controller D having been mechanically placed in its middle position; and these pole changer coils shift the block 10 of the circuit controller C from its existing extreme position to the other extreme position, thereby supplying current to the operating motor, with its field and armature connections reversed, and causing the motor to operate in the other direction and return the switch points to their former position. During such operation of reversal in mid-stroke, the indication selector is shifted in the same way as at the beginning of a normal or reverse operation. The possibility of the operator causing reversal of the switch machine in mid-stroke is characteristic of this particular type of system, and is a feature taken into account in cona rmen nection -with'thedetector flocking scheme embodying the present invention;lpsrovisions being i made for the reasons hereinafter explained "to"prevent such reversal when "the detector track circuit is occupied. 1 This end is accomplished because the indication selector must respond, in the case of suchreversal in mid-stroke, the sa me as in the case' o'f' initial operation from a norrna'l or reverse position, i before current is supplied to the operating inotor rsufiicie-nt to operate the 'switch machine, and since the indication selector: can not respond when the relay R isideenergized due to the presence =of a train in '1 the :detector track'circuit, :it is evident that theopera'tor can not reverse the *switch in mid-stroke after a train vhas entered the track circuit.

=WVhi'le the detector "locking-provided by thisinvention in a sense 'aflords the -same protection as the usual lever lock and' consequently may be used instead of such lever lock, itis considered to' heipreferalole un der ordinary conditions to retain the lever lock. For one thing,:s'uch-lever clocks; when the locking notches are cut in the lev'eraccordingly, will prevent return of the lever from an indication position, when a train occupies the detector track circuit; soltlia't the operator cannot carelessly or thoughtlessly push back his'le'ver', after having initiated .a cycle of operation iof'the-"switch machine, :and interrupt the supply =01: ourrent to the operating motorat 'the 'lever contacts before the switch has had chance to complete its operation. in other words,

' @the :lever lock "can 'be' :used' to prevent the operator from stopping a switch machine in mid-stroke when there'i's va train on the detector track circuit. I lVhile one specific construction of devices and arrangement of circuits, designed -for use in connection with "one particular type of electric interlocking system, has'lo'een selected for disclosure of: the nature and scope ofthis invention; it will'be evident that various inodifications and adaptations of this specific einbodiment shown and described TIIELTY'HOG made :in practice without departing from the invention; and I desire to h ave i t understood that the specific disclosure is merely illustrative; -and does not exhaust the various forms 'ofmeans constituting' the invent-ion; What I claimis';

- 1. Inn-an electric"interlockingwsystem; n switch-machine having two wires-over which operating current is :conducted :a detector .tra-c-k circuit; electromiagnetic device h-aving two high resistance toils-alternately in-' eluded in with said wires, s'aid de- Nl'GE including circuit controlling means top- .era ted uponvenerg izaition '01": 1; either of rsaaid coils i -to establish ".3, i low sresistance :s'hun't around-the energized coil; ahdeutemt means cgozverned by IS'ald track circuit for controlling fthe operation o f'said device.

:2. eln an electric interlocking system, the combination'with a "detector track circuit, a switch :inachine having normal and 're verse operating wires, a dead'-beatiarniature controlling the supply o'f operating current over 'said' wires alternately, "and ielectr'o-Inagnetic means responsive $0: the condition of said detector trackcircuit for actuating said armature. I i 3; 1 In "an- K electric interlocking system the combination with; :a r detector track circuit, a sswitch \nrachine 7 having normal "and I reverse operating circuits, a circuit controller for alternately controlling the supply iof current over said circuits and f adapted to continue in the =.e'x"-isting-' eondition until forcib'ly changed, electro magneticmeans :for; ope'rating 'said circuit controllen and an energizing -circu i't for said electromagnetic means governed by said -track circuit.

4. 111 an electricinterlocking system, the combination with afdetec't'or track circuit; a switch machine having normal and reverse operating 'circi its;-:a circ'uit' controller alternat'ely controlling the supply of current over said-circuits) higlrresistancecoils for --operating said circuit Fcont'roller; included one in each :of said operating'Icireuits, and limiting the flow of a'current therein below that'required to operate "the' switch machine, said operating circuits having their .irfitia'l 'energization controlled I by the -detector track circuit, and a 'dead 'beat armature "op- 'erated ?by saidqc'o ilsand establishing a low resistance "shunt for -"each' coil in turn as the armature is shifized'floy that coil.

7 'Inwan electric interlocking system, the -coinbinati on v-with a "detector track circuit, an electrically operablefswitch machine; a source of current and lever for governing the operation of s'aid' switch rnac'hine, in- 'dicati'on mechanism for the-lever, two con- "trol wires 'between the lever and the switch machine and used alternately for conducting'zoperating current andindication ourrent; an indication selector having high re; sistan'c coilsincluded in-circ'uit' with said control wires respectively, 1 saidindication iselectorw'haviirg a deadfloeat armature, circuit; controllingmeans governed by the detector track circuit itor controlling the ourselectorg-vand means zac-tuated by said armatur e ztor clo'sing a low resistance shunt for said circuit controlling means-and the coil shitting' the armature; v

6. Inan electric interlocking systennthe combination :a' detector track circuit, a switrhflmachine; a source' of'ciurent and a lever at a central control point for govemin-g the e eratienof therswitch machine, insane at sa'id control p'oint governed by: the etectorowl: ir' dait formpnevent'mg the application of power to the switch machine while said track circuit is occupied, and electro-magnetic means comprising a deadbeat armature and two coils alternately energized from said source as the lever is shifted for continuing the supply of power to the switch machine independently of the track circuit after the switch machine has once commenced a cycle of operation.

7. In an electric interlocking system, the combination with a detector track circuit, a switch machine, and means comprising a dead-beat armature and two high resistance coils and governed by the detector track circuit for controlling the supply of operating current to the switch machine.

8. In an electric interlocking system of the type described, the combination with a detector track circuit and a switch machine, of an indication selector having high resistancecoils, circuit controlling means governed by the track circuit for controlling the operation of said indication selector, and means actuated by said selector for determining the supply of effective operating current to the switch machine.

9. In an electric interlocking system of the dynamic indication type, the combina tion with a detector track circuit, of an electrically operable switch machine adapted to generate an indication current dynamically after each operation, a source of current and a lever for controlling the operation of the switch machine, indication mechanism for the lever, an indication selector having high resistance coils and adapted to control the continuity of the in dication circuits over which said indication current flows to the indication mechanism of the lever, circuit controlling means governed by the detector track circuit for controlling the operation of the indication selector, and'means actuated by said selector for establishing a low resistance shunt for said circuit controlling means and the coil of the selector then acting.

10. In an electric interlocking system of the type described having an indication selector with high resistance coils limiting the flow of operating current below that required to operate the switch machine of the system, the combination with a detector track circuit, of circuit controlling means governed by said track circuit and included in circuit with the coils of said selector, and means governed by said selector for establishing a low resistance shunt for said circuit controlling means and its correspond ing coil.

'11. In an electric interlocking system of the type described having an indication selector with high resistance coils and in which the operation of said selector is necessary after each movement of the switch machine in order to obtain an indication,

the combination with a detector track circuit, of a relay governed by said track circuit and controlling the operation of said indication selector, and automatic means actuated by said selector for maintaining the supply of operating current to the switch machine independently of the condition of the detector track circuit.

12. In an electric interlocking system, a switch machine, a lever controlling the op eration of said machine, a detector track circuit, an electric lock for said lever governed by said track circuit, an indication selector, and means governed by the indication selector and by said detector track circuit for controlling the supply of operating current to the switch machine.

13. In an electric interlocking system, a switch machine, a lever controlllng the operation of the switch machine, a detector track circuit, an electric lock for said lever governed by said track circuit, and means governed by the track circuit and acting independently of said lock for preventing the application of effective operating current to the switch machine while said track circuit is occupied.

14. In an electric interlocking system, a switch machine, a lever controlling the op eration of the switch machine, a detector track circuit, an electric lock for said lever governed by said track circuit, and means governed by said track circuit and acting automatically and independently of said lock to prevent application of operating current to the switch machine while said track circuit is occupied but permitting the switch machine to complete a cycle of operation once started prior to the occupancy of the track circuit.

15. In an electric interlocking system, a switch machine, a lever controlling the op eration of the switch machine, a detector track circuit, an electric lock for said lever governed by said track circuit, normal and reverse control circuits for the switch machine governcd by said lever and used alternatelyfor conducting operating and indication currents, and an indication selector controlling the supply of operating current and also the continuity of each indication circuit in turn, said indication selector having its operation governed by said track circuit and acting automatically to prevent the application of effective operating current to the switch machine while the track circuit is occupied but continuing such supply of current independently of said track circuit after the switch machine has commenced a cycle of operation.

16. In an electric interlocking system, a switch machine, a source of current and a lever at a central control point for governing the operation of the switch machine, a detector track circuit, automatic means in cluding a relay at said control point for preventing the supply of operating current to the switch machine while the track circuit is occupied, said means permitting the switch machine to complete a cycle of operation once started prior to the occupancy of the track circuit, and an electric lock governed by said track circuit for preventing reversal of the lever while the track circuit is occupied.

17. In an electric interlocking system, the

' combination with a switch machine, its control lever, and an indication selector having high resistance coils, of an electric lock for the lever, and track circuit control means for governing the operation of the indication selector and alsosaid electric lock.

18. In an electric interlocking system, the combination with a detector track circuit, a switch machine having a normal and a reverse control circuit, a manually operable lever for alternately closing said circuits at one point, and automatic means for alter nately closing said circuits at another point, said automatic means being rendered effective by the movement of the lever to close the same circuit closed by said lever only if said detector track circuit is not then occupied.

. 19. In an electric interlocking system, the combination with a detector track circuit having the usual track relay, a switch machine, a normal and a reverse control circuit for said switch machine each of which may be open at two points, a manually op erable lever for alternately closing said circuits at one point, and automatic means depending ifor its operation on the energization of said track relay for alternately and separately closing at the other point the same circuit closed at the lever.

20. In an electric interlocking system, the combination with a detector track circuit having the usual track relay, a switch machine, anormal and a reverse control circuit for said switch machine each of which may be open at two points, a manually operable lever for alternately closing said circuits at one point, and automatic means depending for its operation on the position of said lever and the energization of said track relay for closing at the other point the same circuit closed by thelever provided the track circuit is then not occupied, said automatic means it once actuated remaining in its actuated position until again changed irrespective of the occupancy of the track circuit.

In testimony whereof I hereby afiix my signature.

WINTHROP KEITH HOWE. 

